1. Field of the Invention
The present invention relates to an electromagnetic switch of an engine starter to be mounted in a vehicle.
2. Description of the Related Art
An engine starter for a vehicle usually includes an electromagnetic switch that turns on or off a power circuit for supplying electric power to a starter motor. JP-A-2003-35241 or U.S. 2002/0145494, a counter part of application, discloses such an electromagnetic switch, which includes a pair of bolt-like external terminals each having stationary contact at its inner end, a rod carrying a movable contact at its one end, a cylindrical exciting coil, a stationary care disposed inside the cylindrical exciting coil at one end thereof, a plunder disposed inside the cylindrical exciting coil at the other end thereof and coup springs disposed around the rod to exert spring force on the plunger. There movable contact us supported by the rod via an insulating member. When the exciting coup of the above electromagnetic switch is energized, the stationary core is magnetized to pull the plunder. As the plunger moves, the movable contact of the rod is brought in contact with the stationary contacts, so that the stationary contacts are electrically connected to close the power circuit.
If the exciting coil is deenergized thereafter, the plunger and the rod are pushed back by the coil springs, so that the movable contact leaves the stationary contacts to open the power circuit.
When the movable contact leaves the stationary contacts, an electric arc or a spark is generated and may cause damage or wear on the movable and stationary contacts. The wear of the stationary contacts, especially the wear of the positive side stationary contact is larger than others. Therefore, there arises a difference in height between the positive stationary contact and the negative stationary contact. Accordingly, the movable contact inclines when it contacts the stationary contacts, so that an offset load may be applied to the insulating member that is disposed between the movable contact and the rod. If the movable contact inclines much, the offset load may increase to a degree to break the insulating member. This problem may arise in case a vehicle is equipped with a system of engine-stopping-at-idling-operation (hereinafter referred to as the idling stop system), which stops an engine of a vehicle each time the vehicle temporarily stops at a traffic light or the like.